Existing direct acting tappets consist of an outer cylinder which is held in a bore in the cylinder head. It is contacted on one end by the camshaft and on the other by the valve. It is allowed to slide axially within the bore, translating the rotary motion of the camshaft into axial motion to the valve. The inside of this outer cylinder is large enough in diameter to surround the engine valve spring.
They also contain an inner cylinder which holds a miniature hydraulic lash compensating element. These two cylinders are connected using a radial cross member which is roughly perpendicular to the axis of the cylinder. This cross member effectively closes off the area between the two cylinders on either end. This can be done using one or two pieces, and is normally done using a low cost material.
A wear resistant cap is then affixed to the end of the part facing the camshaft. In some applications the camface is integral with the outer cylinder and the perpendicular cross member is integral with the inner cylinder and is attached to the outer cylinder. In other designs the inner and outer cylinders are integral with an attached camface cap. In other designs the cylinder extends past the perpendicular cross member and captures the cap which is supported on the cross member.
The joining methods for such tappets include welding, brazing, and staking (mechanical deformation). Because of the difficulty in joining steel to aluminum, proposed aluminum designs for this shell have been of the type using a perpendicular cross member which extends between the lash adjuster and the camface. The camface is simply held in place by the outer cylinder and the valve spring preload.
Engine oil is supplied to the hydraulic lash compensating unit through a cavity or reservoir between the outer and inner cylinders. This cavity is bounded by the camface on one end and by the perpendicular cross member on the other. This cavity is filled from a hole in the outer cylinder which is in contact with pressurized engine oil. The outer cylinder is either coated or heat treated to prevent wear from contact with bore in cylinder head.
In such tappets a major disadvantage is that the body of the tappet must be machined or cast in order to provide the perpendicular portion. Other disadvantages of the hydraulic tappets is that they are heavy, costly to manufacture, have multiple pieces, and are noisy in operation.
Among the objectives of the present invention are to provide a direct acting hydraulic tappet and a method of manufacturing which is lighter; lower in cost; easier to manufacture; quiet in stop-start tests; which can use a steel or cast iron camface; and which can be made of aluminum.
In accordance with the invention, a direct acting hydraulic tappet including a one piece body shell having an outer cylinder, an inner cylinder and a plurality of integral axially extending webs that connect the outer cylinder and the inner cylinder. A cam face member is attached to one end of the body. An oil hole extends from the outer surface of the outer cylinder through one of the webs to an inner surface of the inner cylinder. The hydraulic lash compensating unit is positioned in the inner cylinder. The body shell is made from an extruded length of aluminum and is preferably coated with a Teflon impregnated anodized coating. The cam face is made of steel, cast iron or ceramic and is attached to the one end of the body shell by electromagnetic deformation or by the use of adhesive.